There are a variety of compositions and processes to make precast and cast-in place lightweight cementitious articles. Some of these use lightweight fillers and aggregates to achieve lightweight. Some reduce their density by filling the cement body with tiny gas bubbles. There are many ways to make lightweight cement containing gas bubbles. One of the most common methods is aeration. Aeration can be done mechanically by foaming a freshly prepared cement slurry containing a foaming agent and a foam stabilizer. Another way to aerate cement is to add a pre-generated organic foam into a cement slurry.
To generate lightweight cement with good texture and mechanical performance by the aeration of conventional cement is generally difficult. This is due to the bubble collapse in the slow hardening process of the cement after hydration. Yet another cause for the collapse of cement bubbles is the incompatibility between the organic prefoam component and the inorganic cement slurry component. This latter collapse usually takes place immediately after the contact of the prefoam with the slurry.
U.S. Pat. Nos. 4,113,913; 4,441,944 and 4,559,263 describe foamed cementitious products using high levels of polymers to enhance mechanical strength. U.S Pat. No. 4,731,389 discloses the stabilization of cementitious foam by the interaction between a polyvinyl alcohol modifier and a salt additive such as sodium metaborate. U.S Pat. No. 3,867,159 describes the formation of lightweight concrete using low levels of water soluble polymeric cement binder with a proteinaceous foaming agent.
U.S Pat. No. 3,834,918 describes a raw batch for forming porous architectural structures using high water/cement ratios and water soluble foam stabilizers such hydroxpropyl methyl cellulose, polyvinyl alcohol, or salts of poly(acrylic acid) or poly(methacrylic acid).
U.S Pat. No. 4,473,406 describes unfoamed cementitious compositions having improved flow characteristics by incorporation of copolymers of ethylenically-unsaturated carboxylic acids and hydroxy alkyl esters.
U.S Pat. No. 4,792,360 describes unfoamed cement compositions comprising cement and polymers or copolymers of hydroxyalkyl (meth)acrylates.
U.S. Pat. No. 4,425,291 describes foamed alkali metal silicates using a surfactant and an aqueous natural latex dispersion for water-proofing.
U.S. Pat. No. 4,596,834 describes a foamed cementitious pipe insulation material using mineral acids as foam stabilizers.
British Patent No. 1,381,290 describes lightweight foamed magnesia cement modified with a polymer latex and using water-soluble silicone to stabilize the foam.
Japanese Kokai No. 63-248,782 discloses lightweight aerated cement products using hydroxycarboxylic acid, polyhydric alcohol, polycarboxylic acid salt, lignin sulfonic acid salt/polyol, methyl cellulose and gelatin.
The present invention provides improvements over the techniques used in the prior art to give foamed cementitious compositions which have improved foam stability, improved mechanical strength, improved water resistance and improved sound and thermal insulation.